This invention relates to an apparatus for the transmission of information to a subject through application of electric stimuli, which apparatus effects transmission of information by causing a stimulator to generate pulse signals in conformity with the information and allowing the pulse signals to be conveyed to the skin of the subject only through the selected ones of an array of electrodes attached to the skin.
Efforts are being made to utilize the system of transmission of information by the medium of electrocutaneous stimuli to the human organism as a means of facilitating the operation of prosthetic arms or manipulators by the user by enabling the sensation of touch or sensation of force to be fed back to the user or as a means of providing deaf and/or blind persons with substitutive audio and/or visual sensation, respectively.
Generally in the transmission of information by the electrocutaneous stimuli, a relevant collection of signals is issued in the form of a train of pulses which carries the information in terms of the frequency of repetition of certain pulses, the height of pulses, the width of pulses or the duration of the train of pulses. In the transmission of information by the method described above, if a set of signals desired to be transmitted is converted into a train of pulses and delivered in that form to the skin of the human subject, the magnitude of sensation caused in the skin by the same pulse signals may vary from time to time because of variations in the subject's cutaneous impedance. For this reason, there are times at which the method fails to provide correct transmission of information. The present inventors conducted a study in search of a solution to this problem. They, consequently, ascertained that pulse signals differing in pulse height or pulse width, in the case of information transmission by electrocutaneous stimulation on the human skin, generate thereon one and the same magnitude of sensation when the products of pulse widths multiplied by the squares of respective pulse heights are equal. Based on this knowledge, they suggested a method for correct transmission of information (U.S. patent application Ser. No. 781,887) which comprises preparatorily measuring the cutaneous impedance of a given subject and, on the basis of the results of this measurement, making a necessary correction in the pulse height or pulse width of the pulse signal so as to represent the information to be transmitted, while eliminating the effect of the cutaneous impedance change of that particular subject and ensuring correct transmission of the information.
Since different pulse signals generate the same magnitude of sensation on the human organism when the products of pulse widths multiplied by the squares of respective pulse heights are equal, the only physical parameters that are available for electrocutaneous communication are frequency, energy and duration time of the electric pulse. However, if these parameters alone in electrocutaneous communication are used, maximum capacity of information to be transmitted is from 3 to 5 bits in each case. For a larger amount of complicated information to be successfully transmitted, therefore, it becomes necessary to expand the region of the organism subjected to electrocutaneous stimuli, i.e. to set a multiplicity of electrodes on the subject's skin.
When electric signals are conveyed to the skin through a multiplicity of electrodes attached to the skin, it is necessary that each of the electric routes should be provided with an electric stimulator and an isolator (as disclosed in U.S. Pat. Nos. 3,848,608 and 3,646,940, for example). To ensure independence of the individual electrodes, it is necessary that each of the electrodes should be provided with an isolator.
Where complicated information is to be transmitted by use of a multiplicity of electrodes as described above, the operation is not only uneconomical because of the inevitable use of a multiplicity of expensive parts but also quite hazardous because of the possible simultaneous application of electric signals through the multiplicity of electrodes and the consequent instantaneous transmission of a large electric energy to the human organism.
An object of the present invention is to provide an apparatus for use in the system which transmits information in the form of electric stimuli to the subject through the medium of a multiplicity of electrodes attached to the subject, which apparatus is simple in construction and is capable of accurately conveying information of high complexity.
Another object of the present invention is to provide an apparatus for the transmission of information in the form of electric stimuli to the subject, which apparatus enables complicated information to be conveyed to the subject accurately without jeopardizing the safety of the subject.